Polyamide resins represented by nylon 6 and nylon 66 and polyester resins represented by polyethylene terephthalate and polybutylene terephthalate have high mechanical, oil resistant, electrical insulating and other properties and are used in fabricating a variety of shaped articles such as automobile parts, electric and electronic parts, mechanical parts and the like while taking their advantage. When flame retardancy is required, a halogen-containing flame retardant is incorporated to the resin compound.
Unlike thermoplastics of versatile use represented by polystyrene, polyethylene and polypropylene, polyamide and polyester resins require a process temperature higher than 250° C. for dispersing the flame retardant in the resin compound owing to their high melting points. The flame retardant to be incorporated in polyamide or polyester resins should naturally remain stable during the processing at such a high temperature and, therefore, brominated polystyrene and brominated polyphenylene ether are usually used. However, the resins themselves often darken in brown during the processing with the flame retardant at such a high temperature, particularly in the presence of air or oxygen.
Some antioxidants such as hindered phenols, phosphorus- or sulfur-containing antioxidants are known to be effective to prevent oxidative deterioration of various resins. Such antioxidants are, however, effective to prevent spontaneous and slowly progressive oxidative deterioration of fabricated articles during a long term use thereof but not effective to satisfactorily prevent darkening of the resin during the processing with the flame retardant at a high temperature for relatively short period of time.
JP-A-02142852 discloses a flame retarded polyamide resin composition comprising polyamide resin, halogenated polystyrene or halogenated polyphenylene ether and hydrotalcite or a magnesium and aluminum-containing inorganic compound. JP-A-06345963 discloses a flame retarded polyamide composition comprising nylon 46 resin, brominated styrene homo- or copolymer, and hydrotalcite. It was found that hydrotalcite or other Mg and Al-containing inorganic compounds are not sufficiently effective to prevent darkening of polyamide resin in the presence of a flame retardant during the processing at higher temperatures and may have an adverse effect on the strength property of fabricated articles when used in a large amount. The foregoing problems are found also in polyester resins.
Accordingly, a need remains to exist for providing a flame retarded polyamide or polyester resin composition which is free from disadvantages of the prior art.